Packaging substrates are obtained by cutting a large size wiring substrate into dices of a predetermined size. The large size wiring substrate is formed by laminating wiring layers and insulating layers on a core substrate.
Core substrates recently used for packaging substrates include ones which are made of materials exerting good electrical properties but having brittle cut surfaces when diced. When producing a wiring substrate, an insulating layer and a wiring layer are laminated a plurality of times on a core substrate. These insulating layers and wiring layers respectively have linear expansion coefficients different from that of the core substrate. It is known that this difference in linear expansion coefficient, being coupled with temperature change, increases difference in expansion between the insulating layers, the wiring layers and the core substrate, and generates stress in the outer periphery of the core substrate. If the material used for the core substrate is brittle, cracks may occur in the core substrate. In the case of a laminate including a glass substrate as a core substrate, if the glass substrate has a thickness of more than several tens of micrometers, the glass substrate may split at the end faces.
Cracks that have occurred in a core substrate may split the core substrate. Specifically, immediately after dicing or in the processing after dicing, the internal stress accumulated in the core substrate may be released from such cracks, causing splits in the direction in which the core substrate breaks.
As a dicing method not developing such cracks, for example, a metal layer is formed on a core substrate, at portions corresponding to the outer circumferential portions of packaging substrates, and, after dicing, the exposed metal layer is etched away to create a groove defined by the core substrate and the insulating layer. This groove can minimize the stress applied around the outer periphery of the core substrate. Thus, breakage of the core substrate is effectively decreased or even minimized with a simple configuration. (E.g., see PTL 1).